diff --git a/py/formatfloat.c b/py/formatfloat.c
index 35cd5d51af..b61a958a25 100644
--- a/py/formatfloat.c
+++ b/py/formatfloat.c
@@ -30,6 +30,7 @@
 #include <assert.h>
 #include <stdlib.h>
 #include <stdint.h>
+#include <math.h>
 #include "py/formatfloat.h"
 
 /***********************************************************************
@@ -82,7 +83,6 @@ static inline int fp_isless1(float x) { union floatbits fb = {x}; return fb.u <
 #define FPROUND_TO_ONE 0.999999999995
 #define FPDECEXP 256
 #define FPMIN_BUF_SIZE 7 // +9e+199
-#include <math.h>
 #define fp_signbit(x) signbit(x)
 #define fp_isspecial(x) 1
 #define fp_isnan(x) isnan(x)
@@ -122,7 +122,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
         }
         return buf_size >= 2;
     }
-    if (fp_signbit(f)) {
+    if (fp_signbit(f) && !isnan(f)) {
         *s++ = '-';
         f = -f;
     } else {
diff --git a/tests/float/complex1.py b/tests/float/complex1.py
index 8544105453..479b4b3485 100644
--- a/tests/float/complex1.py
+++ b/tests/float/complex1.py
@@ -59,6 +59,7 @@ ans = (-1.2) ** -3.4; print("%.5g %.5g" % (ans.real, ans.imag))
 
 # check printing of inf/nan
 print(float('nan') * 1j)
+print(float('-nan') * 1j)
 print(float('inf') * (1 + 1j))
 print(float('-inf') * (1 + 1j))
 
diff --git a/tests/float/float1.py b/tests/float/float1.py
index 137dacc233..c64f965a7d 100644
--- a/tests/float/float1.py
+++ b/tests/float/float1.py
@@ -21,6 +21,7 @@ print(float("INF"))
 print(float("infinity"))
 print(float("INFINITY"))
 print(float("nan"))
+print(float("-nan"))
 print(float("NaN"))
 try:
     float("")